Light quark mass ratio from the Dalitz plot of η → π+π-π0 decay

High statistics Dalitz-plot distribution of {eta}{yields}{pi}{sup +}{pi}{sup -}{pi}{sup 0} decay obtained recently by KLOE collaboration is fitted to the results of corresponding theoretical calculations in Chiral Perturbation Theory (ChPT) with unitarity corrections taken into account. The quark mass ratio Q={radical}([m{sub s}{sup 2}-(m{sub d}+m{sub u}){sup 2}/4]/(m{sub d}{sup 2}-m{sub u}{sup 2})) can be obtained from this analysis. We get Q=22.8{+-}0.4 which differs from the value Q{sub DT}=24.2 that follows from Dashen's theorem and agrees with recently calculated electromagnetic kaon mass difference.